Variable resistor construction



Jan. 26, 1960 M. E. BouRNs 2,922,976

VARIABLE REsrsToR CONSTRUCTION Filed Nov. s, 1957 Mhlmhnnnnnnnnnlfigaf 4 I7 4o L" 3 2li) [2O 4| 4| '91 e pas fla 1Q 46" 35 |2- 34 4 s le Ils; NIS el I 3o 3a 24 :2464J 63J F/G- 5 33 Flaa 32 IO 37 rlilllllllrln -41 ,-79 5| o 54 5' 4' 4 may. I4 2 66 l 6 44 k H "66 '2 25 F165 FIG. l0

mvENToR MARLAN E. BOURNS AGENT United safes Pat-enr O 2,922,976 y l VARIABLE REsIsroR CONSTRUCTION Marian E. Bourns, Riverside, Calif. Application November 8, 1957, Serial No. 695,285

1 Claim. (Cl. 338-176) The present invention relates to new and improved variable resistor constructions, and is a continuation-inpart of my pending application, Serial No. 427,326, led May 3, 1954, now U.S. Patent 2,831,949, entitled Variable Resistor Constructions.

The primary object of the present invention is to provide a new and improved variable resistor, or potentiometer, of the type wherein a contact is moved lengthl ce. l 2,922,976

Patented Jan. `26, 1960 is a terminal tab 32, which passes through an opening wise ofa resistance element by means of an adjusting leadscrew.

, More specifically, one of the objects of theinvention is to provide a new form of .slider that is shifted by the leadscrew, and an improved arrangement for securing the contact to the slider.

` These and other objects and advantages of the present invention will become apparent to those skilled in the art,`upon consideration of the following detailed description, together with the accompanying drawings, wherein: i Figure 1 isa side elevational view of a variable resistor embodying the principles of the invention; n

Figure 2- is a cross sectional view of the same, taken at 2-2 of Figure 1; Q

Figure 3 is a cross sectional view, taken at 3-3 of Figure 2;

Figure 4 is a fragmentary sectional view, taken at line 4 4 of Figure 2; l

Figure -5-'is another fragmentary sectional view, taken at 5-5 of Figur 2;

Figures 6 and 7 are perspective views of the slider and contactusedin'the instrument of Figure l, showing more clearly the specific arrangement for securing the contact to the slider;

Figure 8 is a cross sectional view similar to Figure 3, showing a modified form of the invention;

Figure 9 is a similar cross sectional view of still another form of the invention;

Figure 10 is a sectional view, taken at 10-10 of Figure 9; and

Figure l1 is a fragmentary sectional view, showing the manner of connecting one of the terminal lugs to the resistance element.

First to be described willbe the embodiment shown in Figures 1 to 7, inclusive, of the drawings. The variable resistor is designated in its entirety by the reference numeral 10, and comprises a body 11 of nonconductive material such as plastic, ceramic, or the like, having a channel-shaped lid or cover l wrapped around three sides thereof. The body 11 is provided with a substantially ilat upper surface 12 and upstanding ends 14. The sides 15 of the body are recessed at 16 and 17 to receive the side v walls 19 of the U-shaped cover 20. 'I'he top section 21 of the cover 20 is disposed generally parallel to the flat upper surface 12 between the ends 14 of the body member 11, and overlies the ends 14, to which it is secured by means of tabs 22 that extend down over the ends `of the body within notches 23. At the bottom side of the body, the tabs 22 are turned under, as shown at 26, and are seated within cavities 25.

33 in the bottom of the body 11.

Parallel to the channel is another channel 34, which holds a resistance element 36. The element 36 consists of resistance wire wrapped around a nonconductive card or mandrel 35, and the element-is normally held in place by means of terminal tabs 37 projecting through apertures 38 in the bottom of the body 11. The tabs 37 are preferably bowed slightly, as shown at 39 in Figure 2, so that they are held within the apertures 38 by spring tension.

Disposed between the cover 20 and the body 11 is a slider, or carrier 40, having a U-shaped contact member 44 on the underside thereof which wipes on both the conductor 31 and resistance element 36. As best shown in Figures 6 and 7, the carrier 40 comprises a generally rectangular shaped block of nonconductive plastic, having an internally threaded bore 41 extending through from one end to the other. The threaded portion 51 of the leadscrew 50 is screwed through the bore 41, to provide a driving connection for shifting the slider 40 lengthwise of the leadscrew when the latter is turned.

Formed in the sides of the slider A40 adjacent one end A thereof are narrow, vertical slots 42 which receive upwardly projecting ears 43 of the-contact member 44. It will be noted in Figure 7 that the space between the ears 43 is in the form of a generally circular notch; the gap at the top being somewhat less than the diameter of the circle. The bottom of the notch 42 in the slider 40 is also circular in cross section and is concentric about the bore 41. The bottom of the notches 42 is approximately the same diameter as the circular notch in the ears 43, so that the ears 43 seat snugly within the notches 42, and provide a rm grip on the slider 40 for the contact 44.

The leadscrew 50 is in the form of an elongated shaft having a threaded center section 51 and smooth ends 52 and 53. The end 52 is rotatably supported within a cavity 54 in the left-hand end 14 of the body; while the other end 53 is seated within a notch 56 in the righthand end 14 and projects beyond the end of the body. End 53 of the shaft is held against endwise movement by an inwardly projecting flange 57 in the notch 56, and by means of a similar projection 58 (see Figure 4) extending downwardly from the top 21 of the cover 20. Projections 57 and 58 engage a shoulder, which may conveniently be provided by a circumferential groove 55 in the shaft 50.

At the other end of the shaft 50, a projection 59 extends downwardly from the top 21 of the cover and bears against the smooth portion 52, as best shown in Figure 5. Both of the projections 58 and 59 exert a slight pressure on the shaft so as to provide a certain amount of frictional resistance to rotation. With this arrangement, the slider 40 and the contact member 44 are moved length- Wise of the resistance element 36 and conductor 31 by rotating the leadscrew in one direction or the other. The slider 40 is prevented from turning with the shaft 50 by means of runners, or lugs 63, which project downwardly from the underside of the slider 40 and slidably engage the exposed sides of the conductor 31.

The modified construction shown in Figure 8 of the drawings differs from that shown in Figures l through 5 in that the conductor and resistance element are in the form of a metal strip 64 and a strip 60 of resistive composition material or the like, both of which are disposed within parallel grooves 61 in the body member 11. Another diiference in the construction of Figure 8 is that I of the leadscrew is resiliently gripped by the spring clip.

the body 11,'and include bent-over spring contact portions that overlie the conductor 64Vand element 60, and

Y make electrical contact with the top nsurfaces thereof.'

With this Specific construction, the tab employed with the conductor strip 64 is located adjacent tor one efndthereof;y so as not tol interefere with the movement vof thecontact 44. f Y l Y Another form of the invention is shown in Figures 9 and 10, which particularly illustrates a yieldable driving connection between theleadscrew and the slider 46. ln this form of the inventionterminal tabs 65 are molded within the body 11 so as to project above the top surface 12, and are bent over at right angles to overlie resistance films 66, which are-positioned upon supporting bases 67 of nonconductive material seated within slots 68. The tabs 65 may be soldered, as shown at 69, to the resistance film.

The slider 40 employed with the modied construction shown in Figures 9 and 10 diiersfrom those previously described, in that the bore 41 is somewhat oversize and is not threaded. Extending down into the slider 40 from the top side thereof is a cavity 71, which extends below and intersects the bore 41.

Seated within the cavity 71 is a V-shaped spring clip 72. having sides 73 and 74 that are joined at an apex 75. Both of the sides 73, 74 are provided with holes, 76 and 77, respectively, which are of such a dimension thatV when the sides 73, 74-arebent together, the shaft 50 passes freely through the holes without having tok screw the shaft through the holes, as is necessary with a threaded hole, such as in the embodiment of Figure 2. When the slider has been moved to the 'desired location along the length of the leadscrew, the sides 73, 74 are released, allowing them to spring outwardly. As the sides 73, 74 spread apart, the top and bottom edges of the holes 76, 77 grip the leadscrew on opposite sides thereof, and at least one of the said edges drops down into the thread of the screw portion 51 to provide a driving connection between the leadscrew and the slider. At the Vsame time, the sides 73, 74 engage the edges 78 of the cavity 71 so as to wedge the spring clip 72 against the slider 40 in such a manner that as the shaft 50 is turned, the slider 40 is moved one way or the other along the length of the resistance element.

One advantage of the above-described arrangement is that it substantially eliminates backlash, since the thread yAnother advantage is that the sidesV 73, 74 of the spring clip are capable of yieldingunder excessive force, and

ride up over the threads of 'the leadscrew. Thus, if the slider 40 is moved to the end of its travel in either direction and is abutting against the body, it is impossible to damage either the body or the slider by forcibly turning the leadscrew.

BothA of the sides 73, 74 terminate in bent-over end sections 79, which slidably engage the underside of the top section 21 of cover 20 to prevent the' slider 40* from Y rotating when the shaft 50 is turned. rl`he end sections 79 press against the cover Z0 with'ayieiding spring pressure of su'icient force to resist the torque exerted on the spring clip 72 by the leadscrew.

While I have shown and described certain illustrative forms of the invention in considerable detail, it will be understood that various changes may be made in the shape and arrangement of the several parts without departing from the scope of the following'claim.

I claim:

In a variable resistor having a resistance element,a rotatable leadscrew disposed parallel to said element,V a slider mounted on said leadscrew and having threaded engagement therewith, said slider havinga narrow slot formed therein transverse to its line of travel, the bottoni` of said slot being generally circular in conguration and concentric with the axis of said leadscrew,jand a Contact of resilient sheet metal mounted on said slider so `as to wipe'on said resistance element, said contact Ahaving a pair of upwardly bent, laterally spaced tabs receivedv with in said slot, the space between said tabs being in the form' of a circular cut-.out soas to t the circular bottom of said slot, and the outer ends of said tabs convergingslightly so that'the distance between them is less than the diameter of the bottom of said slot, whereby said tabs are sprung into said slot and resiliently grip the bottom thereof to secure said contact to said member.

References Cited in the file of this patent UNITED STATES PATENTSv Great Britain afsa- Mar. 1.2. 1.95, 

